Yes, I agree with Deru. I don't have anything other than what I would consider an educated guess though. If there is a lot of obstruction, it's definitely possible for the drug to not be efficiently absorbed.
If I'm not mistaken, anything not absorbed through the sinus is going to eventually end up in the stomach. I just don't know exactly how long this process could feasibly take, however.
Most Opioids including Fentanyl and/or Amphetamines have a significantly higher bioavailability relative to the route of administration.
Others have mentioned trying to administer your drugs rectally and I would recommend trying it out. You will still get a higher BA, the onset is pretty similar and a lot of the complications that can potentially arise from insufflation are almost completely negated.
I don't advocate or "recommend" poly-drug use, but it sounds like you are already into it. You might find you enjoy rectal administration better. As opposed to insufflation in which you are limited by the volume of the sinuses, you can pretty much dissolve all of your drugs in one syringe and administer simultaneously.
It's not a difficult process. Just crush your drugs into a powder. Take your oral syringe, preferably with a rectal tip (ask pharmacist, they typically have them for free) and draw up a full barrel of water. In some kind of vessel, mix the powdered drugs and water until you have a uniform solution.
Lay on your stomach or side, insert syringe into your rectum and inject. Slowly remove the syringe and stay prone for 10-15 minutes. I think you'll find that insufflation and rectal administration are pretty similar in terms of onset, time to peak et cetera.
Just let us know if you have any questions.